In the immediate post-war period various companies in the aeronautical sector attempted to resume industrial activities through the conversion of war production. The small and medium power engines, developed between the second half of the 1930s and the early 1940s mainly for trainer aircraft, resulted in line with the new development of general aviation. To this end, Alfa Romeo resumed the project of the 121 engine of 1943, creating a new model with improved performance through the use of a mechanically-driven supercharger and a propeller speed reducer. The 121 engine was produced in three versions, RC14, RC20 and RC22, which differed in maximum power output altitude, respectively equal to 1400, 2000 and 2200 meters above sea level. This was obtained through a different calibration of the supercharging system, according to the needs of the various aircraft. Its design is characterized by the eight-cylinder inverted-V arrangement and by the air-cooling system. The engine is quite compact and light, with performance comparable to that of engines of the same category. Despite this, the production of the Alfa Romeo 121 was interrupted after a reduced number of units due to the commercial failure, or lack of production, of the aircraft which it was designed for.